State of the art research, development and manufacturing often requires accurate measurement of small mechanical displacements. For example, in the design and manufacture of engineered microstructures, accurate surface profile measurements of these microstructures is often required. Stylus profiling instruments are important tools used by the optics, microelectronics, precision machining and other industries for nanometer scale surface metrology. A stylus profiling instrument typically includes a stylus tip which is scanned across a surface profile. The displacement of the stylus tip is measured to measure the surface profile of the scanned surface.
Stylus profiling instruments often mount the stylus on the free end of a cantilever and measure the displacement of the cantilever to obtain a surface profile. Cantilever stylus profiling instruments are described in U.S. Pat. No. 5,015,850 to Zdeblick et al. entitled Microfabricated Microscope Assembly; U.S. Pat. No. 5,193,383 to Burnham et al. entitled Mechanical and Surface Force Nanoprobe; a publication by Neubauer et al. entitled Force Microscopy with a Bidirectional Capacitance Sensor, Review of Science Instrumentation, Vol. 61, No. 9, September 1990, pp. 2296-2308; and a publication by Miller et al. entitled Resonant Phase Shift Technique for the Measurement of Small Changes in Grounded Capacitors, Review of Scientific Instrumentation, Vol. 61, No. 4, Apr. 1990, pp. 1267-1272. In these cantilever stylus profiling instruments, capacitors are often used for position sensing, and piezoelectric actuators are often used for moving the scanning stage and/or cantilever. Another publication which describes a capacitance based position monitor is A Scanning Tunneling Microscope with a Capacitance-Based Position Monitor by Griffith et al., Journal of Vacuum Science Technology, Vol. B8, No. 6, November/December 1990, pp. 2023-2027.
Other stylus profiling instruments use a "rocking-beam" force balance system in which the stylus is placed at one end of the beam which rocks on a central support. Rocking beam stylus profiling instruments are described in a publication by Grigg et al. entitled Rocking-Beam Force-Balance Approach to Atomic Force Microscopy, Ultramicroscopy, Vol. 42-44, 1992, pp. 1504-1508; a publication by Joyce et al. entitled A New Force Sensor Incorporating Force-Feedback Control for Interfacial Force Microscopy, Review of Science Instrumentation, Vol. 62, No. 3, March 1991, pp. 710-715; and a publication by Miller et al. entitled A Rocking Beam Electrostatic Balance for the Measurement of Small Forces, Review of Science Instrumentation, Vol. 62, No. 3, Mar. 1991, pp. 705-709. As described in the Grigg et al. article, the rocking beam may be configured to provide air damping. Rocking beam stylus profiling instruments also use capacitive measurement techniques and piezoelectric actuators. It is also known to use capacitive measurements to overcome hysteresis effects and accurately measure the position of a piezoelectric actuator.
The cantilever displacement in a stylus profiling instrument may also be measured optically. See for example, U.S. Pat. Nos. 5,025,658 to Elings et al. entitled Compact Atomic Force Microscope; 5,144,833 to Amer et al. entitled Atomic Force Microscopy; and 5,210,410 to Barrett entitled Scanning Probe Microscope Having Scan Correction.
Notwithstanding the widespread use of stylus profiling instruments and methods, there continues to be a need for nanometer scale stylus profiling instruments and methods which have low contact force. Low contact force is important in order to prevent damage to fragile microengineered surfaces. It is also important to be able to obtain a surface profile over long ranges of operation, on the order of tens of millimeters, so as to accurately evaluate surface form and finish in accordance with international profiling standards. It is also well known that stylus tips and cantilevers often require replacement, as a result of wear and breakage. In designing a stylus profiling instrument, it is important to allow the tip and cantilever to be easily and rapidly removed, replaced, and realigned.